Darien Richardson, shown here in a picture distributed Monday by the Portland Police Department and her family on Monday died from complications from a a gunshot wound she suffered during a home invasion in 2010.

Judi and Wayne Richardson announce a $10,000 reward for information leading to the arrest and indictment of the person or persons responsible for the early 2010 death of their daughter, Darien, during a news conference at the Portland Police Department on Monday.

PORTLAND, Maine — Portland police said Monday that the 2010 killing of Darien Richardson has become a cold case, and they hope a new $10,000 reward for information will help them find the masked intruder who broke into her bedroom and shot her while she slept.

Portland Police Assistant Chief Vernon Malloch told reporters Monday that investigators believe the key to solving the mystery can be found in the area’s black market for weapons, but have reached a dead end in tracking the history of the gun used to kill Richardson and one other Portlander in separate cases.

“A sad and unfortunate twist in this case is that a little more than a month after Darien and her boyfriend were shot, the same gun was used in a murder on Park Avenue here in Portland,” Malloch said. “That case is solved. We recovered the firearm. We know that it’s the same gun that killed both people. Unfortunately, we don’t know where the gun came from.”

In the second case, Daudoit Butsitsi was convicted of shooting and killing 24-year-old Serge Mulongo and sentenced to 38 years in prison. But Malloch said police do not believe the two shootings are connected other than by the firearm used, which detectives claim was sold to Butsitsi on the region’s shadowy black market, perhaps by the individual responsible for Richardson’s death.

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He said Butsitsi has refused to tell police where or from whom he obtained the gun.

Malloch said Portland police — working with agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives — were able to pinpoint the original 2008 sale of the gun, but lost track of the weapon after the first owner resold it.

“He sold it at a gun show sometime later to a person that he did not identify, with no records check or criminal history check done,” Malloch said. “That’s where the trail ends with that gun, a gun that has now been used to kill two Portland residents.”

Richardson, a 25-year-old South Portland native who graduated from Bowdoin College, was shot while sleeping next to her boyfriend in their 25 Rackleff St. home on Jan. 8, 2010, by a masked intruder or intruders, police say. She died suddenly the following month from a blood clot resulting from the gunshot wound while visiting a friend in Florida.

“Our investigation tells us we’re now fairly certain this shooting was related to the illegal trafficking of prescription drugs, specifically Oxycontin,” Malloch said Monday. “Our investigation does not suggest that Darien had any role in drug trafficking, rather we believe she’s another victim of the violence that can be associated with this.”

Malloch said police do not believe Richardson was aware of the drug trafficking going on among other residents of 25 Rackleff St., and added that investigators have had “varied” amounts of success getting information about the crime and possible perpetrators from her boyfriend at the time, Cory Girard. Girard was hit by the gunfire, but survived the ordeal.

On Monday, Richardson’s parents, Wayne and Judi Richardson, announced a $10,000 reward for information leading to the arrest and indictment of the person or persons responsible for their daughter’s death. They said they raised the money through family and friends, as well as donations made by the public through the website rememberingdarien.org.

“We want these violent criminals off our street,” Judi Richardson told reporters Monday. “It’s not right that such a beautiful, vibrant and wonderful person’s life ended in such a violent way. Darien does not deserve that — no one deserves that. Our hope has always been that someone will come forward with information that will lead to the person who took Darien so violently from this world.”

Police ask that anyone with information that could pertain to this case to contact police at 874-8533 or through www.portland-police.com.